The present invention relates to a liquid jetting head capable of ejecting various kinds of liquid in the form of droplets for use in an ink jet recording apparatus, a display manufacturing apparatus, an electrode forming apparatus, a biochip manufacturing apparatus, etc., and particularly relates to a method and an apparatus for measuring the natural vibration period concerning liquid stored in a pressure chamber, and a liquid jetting apparatus in which the waveform of a drive signal is established on the basis of the determined natural vibration period.
As a liquid jetting apparatus having a liquid jetting head capable of ejecting liquid in the form of a liquid droplet, for example, there has been proposed an image recording apparatus in which ink droplets are ejected to record an image or the like on recording paper, an electrode forming apparatus in which an electrode material in a liquid form is ejected onto a substrate to thereby form electrodes, a biochip manufacturing apparatus in which biological samples are ejected to manufacture biochips, or a micropipette for ejecting a predetermined amount of a sample into a vessel.
To eject a liquid droplet, the liquid jetting head uses a change of pressure in the liquid stored in the pressure chamber. In the liquid jetting head, pressure vibration is excited in the liquid in the pressure chamber with the change of pressure as if the inside of the pressure chamber were an acoustic tube. The period of the pressure vibration is also called a natural vibration period because it is fixed for each kind of liquid jetting head. Then, the natural vibration period can be varied among liquid jetting heads belonging to one and the same kind. This is because there occurs a variation in dimensions or setting accuracy of parts constituting the liquid jetting heads. In accordance with the variation of the natural vibration period, there occurs a variation in droplet ejecting properties such as droplet ejecting amount or flight velocity. This is because the change of liquid pressure differs in accordance with the natural vibration period when the heads are driven by one and the same drive signal, so that there occurs a difference in position or moving speed of a meniscus (free face of liquid exposed in the nozzle orifice) at the time of liquid droplet ejection.
Under such circumstances, there has been proposed an apparatus for measuring the natural vibration period of a liquid jetting head and controlling waveform elements forming a drive signal on the basis of the result of the measurement. Various methods for measuring the natural vibration period have been proposed. However, the productivity will be lowered if it takes long time to measure the natural vibration period. Taking this point into consideration, a method has been proposed in which three kinds of evaluation pulses set to have different time intervals between an excitation signal and an ejection signal are used to classify liquid jetting heads into a plurality of Tc ranks based on liquid ejection amounts corresponding to the respective evaluation pulses (for example, disclosed in Japanese Patent Publication No. 2002-154212A). In this related-art method, it will be sufficient if the ejected liquid amount is measured three times for one liquid jetting head. Accordingly, the work of measurement can be carried out efficiently. Thus, this method is suitable to mass production.
However, in order to further improve the productivity, it is necessary that the measurement of the natural vibration period is made more efficient. In addition, in order to control the amount or the flight velocity of an ejected droplet with higher accuracy, it is desired that the natural vibration period of a liquid jetting head itself is measured.
It is therefore an object of the invention to make the measurement of the natural vibration period more efficient while improving the measuring accuracy of the natural vibration period. It is also one object of the invention to control the amount or the flight velocity of an ejected droplet with higher accuracy.
In order to achieve the above objects, according to the invention, there is provided a method of measuring a natural vibration period of a liquid jetting head provided with a nozzle orifice, a pressure chamber communicated with the nozzle orifice, a liquid supply port which supplies liquid into the pressure chamber, and a pressure generation element which causes pressure fluctuation in the liquid contained in the pressure chamber, the method comprising steps of:
providing a first evaluation signal including a first excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and a first ejection element which follows the excitation element after a first time period to eject a first liquid droplet from the nozzle;
providing a second evaluation signal including a second excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and a second ejection element which follows the excitation element after a second time period to eject a second liquid droplet from the nozzle, which is longer than the first time period;
supplying the first evaluation signal to the pressure generating element to measure a first ejected amount of the first liquid droplet;
supplying the second evaluation signal to the pressure generating element to measure a second ejected amount of the second liquid droplet;
calculating an ejected amount ratio of the first ejected amount and the second ejected amount; and
determining the natural vibration period of the liquid jetting head based on the ejected amount ratio.
According to the invention, there is also provided an apparatus for measuring a natural vibration period of a liquid jetting head provided with a nozzle orifice, a pressure chamber communicated with the nozzle orifice, a liquid supply port which supplies liquid into the pressure chamber, and a pressure generation element which causes pressure fluctuation in the liquid contained in the pressure chamber, the apparatus comprising:
a first evaluation signal generator, which generates a first evaluation signal including a first excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and a first ejection element which follows the excitation element after a first time period to eject a first liquid droplet from the nozzle;
a second evaluation signal generator, which generates a second evaluation signal including a second excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and a second ejection element which follows the excitation element after a second time period to eject a second liquid droplet from the nozzle;
a first evaluation signal supplier, which supplies the first evaluation signal to the pressure generating element to measure a first ejected amount of the first liquid droplet;
a second evaluation signal supplier, which supplies the second evaluation signal to the pressure generating element to measure a second ejected amount of the second liquid droplet;
a calculator, which calculates an ejected amount ratio of the first ejected amount and the second ejected amount; and
a natural vibration period determinant, which determines the natural vibration period of the liquid jetting head based on the ejected amount ratio.
In the above configuration, since it will be sufficient if the amount of liquid is measured twice for one liquid jetting head, it is simple and easy to support the automation of a manufacturing line. It is therefore possible to manufacture liquid jetting heads without reducing the productivity. Thus, the invention is suitable to mass production. Further, since there is a high correlation between the natural vibration period and the ejected amount ratio the natural vibration period of a liquid jetting head subjected to the measurement can be determined with high accuracy.
Preferably, the method further comprises steps of:
providing a plurality of measurement signals, each including an excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and an ejection element which follows the excitation element after a predetermined time period different from another measurement signals to eject a liquid droplet from the nozzle;
providing a first liquid jetting head having a maximum natural vibration period that can be established in a manufacturing process;
providing a second liquid jetting head having a minimum natural vibration period that can be established in the manufacturing process;
supplying the measurement signals to the first liquid jetting head to obtain a first ejected amount fluctuation curve which indicates relationship between input natural vibration periods and output ejected liquid amounts in the first liquid jetting head;
supplying the measurement signals to the second liquid jetting head to obtain a second ejected amount fluctuation curve which indicates relationship between input natural vibration periods and output ejected liquid amounts in the second liquid jetting head;
determining a first time range in which an output ejected liquid amount increases in accordance with increase of an input natural vibration period in both of the first ejected amount fluctuation curve and the second ejected amount fluctuation curve;
determining a second time range in which an output ejected liquid amount decreases in accordance with increase of an input natural vibration period in both of the first ejected amount fluctuation curve and the second ejected amount fluctuation curve;
determining the first time period such that the first ejection element is supplied at a timing in the first time range; and
determining the second time period such that the second ejection element is supplied at a timing in the second time range.
In such a configuration, when the natural vibration period varies, one of the first and second ejected amounts increases while the other decreases. Accordingly, the variation of the ejected amount ratio relative to the unit variation of the natural vibration period can be secured to be larger than any other setting. As a result, the natural vibration period can be determined with high accuracy.
Here, it is preferable that: the first time range continues from one peak point in the first ejected amount fluctuation curve to one bottom point in the second ejected amount fluctuation curve which is adjacent to the one peak point; and the second time range continues from one bottom point in the first ejected amount fluctuation curve to one peak point in the second ejected amount fluctuation curve which is adjacent to the one bottom point.
Further, it is preferable that the method further comprises steps of:
providing a third liquid jetting head having a standard natural vibration period which matches with a designed value;
supplying the measurement signals to the third liquid jetting head to obtain a third ejected amount fluctuation curve which indicates relationship between input natural vibration periods and output ejected liquid amounts in the third liquid jetting head; and
determining the first time period and the second time period such that the first ejection element and the second ejection element are supplied at timings at which the third ejected amount fluctuation curve has a maximum gradient value.
In such a configuration, the variation width of the ejected amount ratio relative to the variation width of the natural vibration period can be expanded to be as large as possible, so that the natural vibration period can be determined on the basis of the ejected amount ratio with high accuracy.
Further, it is preferable that the first time range and the second time range are determined within adjacent fluctuation cycles of the first ejected amount fluctuation curve and the second ejected amount fluctuation curve.
Preferably, the method further comprises steps of:
providing a plurality of measurement signals, each including an excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and an ejection element which follows the excitation element after a predetermined time period different from another measurement signals to eject a liquid droplet from the nozzle;
providing a first liquid jetting head having a maximum natural vibration period that can be established in a manufacturing process;
providing a second liquid jetting head having a minimum natural vibration period that can be established in the manufacturing process;
supplying the measurement signals to the first liquid jetting head to obtain a first ejected amount fluctuation curve which indicates relationship between input natural vibration periods and output ejected liquid amounts in the first liquid jetting head;
supplying the measurement signals to the second liquid jetting head to obtain a second ejected amount fluctuation curve which indicates relationship between input natural vibration periods and output ejected liquid amounts in the second liquid jetting head;
determining the first time period and the second time period such that the first ejection element and the second ejection element are supplied at timings within a time range from one peak point in the first ejected amount fluctuation curve to one peak point in the second ejected amount fluctuation curve which is adjacent to the one peak point.
In such a configuration, the ejected amount fluctuation curve of a liquid jetting head subjected to the measurement exists between the first ejected amount fluctuation curve and the second period ejected amount fluctuation curve. Accordingly, the natural vibration period can be determined with extremely high accuracy on the basis of the ejected amount ratio.
Here, it is preferable that the method further comprises steps of:
providing a third liquid jetting head having a standard natural vibration period which matches with a designed value;
supplying the measurement signals to the third liquid jetting head to obtain a third ejected amount fluctuation curve which indicates relationship between input natural vibration periods and output ejected liquid amounts in the third liquid jetting head; and
determining the first time period and the second time period such that an average value thereof is placed on one bottom point in the third ejected amount fluctuation curve.
Still preferably, a difference between the first time period and the second time period is a half of the standard natural vibration period.
Preferably, each potential difference of the first excitation element and the second excitation element is not less than 90% of each potential difference of the first ejection element and the second ejection element.
Still preferably, each potential difference of the first excitation element and the second excitation element is not less than 95% of each potential difference of the first ejection element and the second ejection element.
Preferably, the method further comprises steps of:
judging whether the ejected amount ratio is within a predetermined value range;
modifying at least one of the first evaluation signal and the second evaluation signal when the ejected amount ratio is not within the predetermined value range; and
measuring at least one of the first ejected amount and the second ejected amount with at least one modified evaluation signal before the step of determining the natural vibration period.
In such a configuration, the natural vibration period of a liquid jetting head can be measured with high accuracy even in a liquid jetting head whose natural vibration period is largely deviated from the designed value.
Here, it is preferable that both of the first evaluation signal and the second evaluation signal when the ejected amount ratio is not within the predetermined value range.
Further, it is preferable that the method further comprises step of updating the ejected amount ratio based on the first ejected amount and the second ejected amount measured with the at least one modified evaluation signal.
Specifically, the first time period is updated to a further shorter third time period when the determined natural vibration period is less than a predetermined value range, and the second time period is updated to a further longer fourth time period when the determined natural vibration period is greater than the predetermined value range.
Preferably, the natural vibration period is determined based on a correlation between the ejected amount ratio and the natural vibration period.
Here, it is preferable that the correlation is provided as a linear expression in which the ejected amount ratio serves as a variable.
Specifically, it is preferable that: a variable range of the ejected amount ratio is divided into a plurality of ranges; and the linear expression is provided with respect to each of the divided ranges.
Here, it is preferable that the divided ranges includes a first range which is less than a standard ejected amount ratio corresponding to a designed natural vibration period, and a second range which is not less than the standard ejected amount ratio.
Alternatively, it is preferable that the divided ranges includes a first range including a standard ejected amount ratio corresponding to a designed natural vibration period, a second range which is less than the first range, and a third range which is greater than the first range.
In such configurations, the natural vibration period can be determined with high accuracy on the basis of the ejected amount ratio.
Preferably, the first evaluation signal and the second evaluation signal are supplied to the pressure generating element at a frequency which is not greater than 10 kHz.
Still preferably, the first evaluation signal and the second evaluation signal are supplied to the pressure generating element at a frequency which is not greater than 5 kHz.
In such configurations, a liquid droplet can be ejected in a stable condition so that the weight of the liquid droplet can be measured with higher accuracy.
Preferably, the method further comprises steps of: measuring temperature of operation environment of the liquid jetting head; and correcting the natural vibration period based on the temperature.
Incidentally, the correcting step includes both the case where the natural vibration period is corrected through the correction of the ejected liquid amount and the case where the determined natural vibration period is corrected directly.
In such a configuration, the natural vibration period can be determined with high accuracy even if the viscosity of the liquid varies in accordance with the environmental temperature.
Preferably, the method comprises steps of: acquiring dimension information regarding at least one of the liquid supply port, pressure chamber and the nozzle orifice; and correcting the natural vibration period based on the dimension information.
Incidentally, the correcting step includes both the case where the natural vibration period is corrected through the correction of the ejected liquid amount and the case where the determined natural vibration period is corrected directly.
Preferably, the liquid is ink comprising a coloring material.
According to the invention, there is also provided a liquid jetting recording head, comprising:
a nozzle orifice;
a pressure chamber communicated with the nozzle orifice;
a liquid supply port which supplies liquid into the pressure chamber;
a pressure generation element which causes pressure fluctuation in the liquid contained in the pressure chamber; and
an indicator, which indicates the natural vibration period determined by the above measuring method.
Preferably, the liquid jetting head further comprises an information storage, which stores the natural vibration period.
Preferably, the indicator is optically readable member.
According to the invention, there is also provided a liquid jetting recording head, comprising:
a nozzle orifice;
a pressure chamber communicated with the nozzle orifice;
a liquid supply port which supplies liquid into the pressure chamber;
a pressure generation element which causes pressure fluctuation in the liquid contained in the pressure chamber; and
an indicator, which indicates the ejected amount ratio calculated by the above measuring method.
Preferably, the liquid jetting head further comprises an information storage, which stores the ejected amount ratio.
Preferably, the indicator is optically readable member.
According to the invention, there is also provided A liquid jetting apparatus, comprising:
the liquid jetting head a nozzle orifice, a pressure chamber communicated with the nozzle orifice, a liquid supply port which supplies liquid into the pressure chamber, a pressure generation element which causes pressure fluctuation in the liquid contained in the pressure chamber, and an indicator which indicates ID information regarding the natural vibration period determined by the above measuring method;
a drive signal generator, which generate a drive signal for driving the pressure generating element; and
a corrector, which corrects a waveform of the drive signal based on the ID information.
In such a configuration, the pressure generating element is driven by the optimized drive signal so that the ejected amount or flight velocity of an ejected droplet can be controlled with higher accuracy.
Here, it is preferable that the ID information is numeric information indicating the natural vibration period or information regarding the ejected amount ratio.
Further, it is preferable that: the liquid jetting apparatus further comprises an information storage, which stores the ID information; and the corrector corrects the waveform of the drive signal based on the ID information stored in the information storage.
Further, it is preferable that: the drive signal includes a plurality of waveform elements including an ejection element adapted to eject a liquid droplet from the nozzle orifice; and the corrector corrects a control factor in at least one of the waveform elements.
Here, it is preferable that: the control factor is a duration of the at least one corrected waveform element; and the duration includes an invariable reference duration and a first duration which is variable in accordance with the ID information.
Here, it is still preferable that the duration includes a second duration which is variable in accordance with temperature of operation environment of the liquid jetting apparatus.
In such configuration, the duration of the waveform element can be easily established arithmetically. Incidentally, the first and second durations may include positive and negative numbers respectively.
Further, it is preferable that the corrected waveform element is a damping element related to damping operation of pressure fluctuation after liquid ejection.
Here, it is preferable that: the waveform elements includes a damping expansion element which expands the pressure chamber to damp the pressure fluctuation after the liquid ejection, and a damping hold element generated between the ejection element and the damping expansion element and having a constant potential; and the control factor is a duration of the damping hold element.
Alternatively, it is preferable that: the waveform elements includes a damping contraction element which contracts the pressure chamber to damp the pressure fluctuation after the liquid ejection; and the control factor is a duration of the damping contraction element.
Still alternatively, it is preferable that: the waveform elements includes an expansion element which expands the pressure chamber to pull a meniscus of liquid in the nozzle orifice toward the pressure chamber, and an expansion holding element generated between the expansion element and the ejection element and having a constant potential; and the control factor is a duration of the expansion holding element.
In such configurations, the damping element is optimized so that the meniscus can be rapidly restored after droplet ejection. Thus, the droplet ejection property at the time of high-frequency driving can be stabilized. Incidentally, the xe2x80x9cmeniscusxe2x80x9d means a free surface of the liquid exposed in the nozzle orifice.
Further, it is preferable that the corrector corrects a reference potential of the drive signal defined as an initial end potential and a termination end potential at a unit driving cycle.